Train chargers are used to supply power to all the DC loads in the train and charge storage batteries. According to different operating conditions of a train, a charger has multiple running modes, specifically including a constant-voltage mode, a charging-current-limiting mode and a total-current-limiting mode. To ensure the stable operation of a charger, each running mode corresponds to different control strategies, that is, a constant-voltage control strategy, a charging-current-limiting control strategy and a total-current-limiting control strategy.
A phase shifted full bridge (PSFB) charger is a charger in which a PSFB converter is used as a soft switch of the charger. The structure of the PSFB charger includes a PSFB circuit, a high frequency transformer and a rectifying circuit, which are connected successively, wherein the PSFB circuit includes a support capacitor and a charging resistor; and an output terminal of the rectifying circuit is connected to the storage battery and loads, respectively, to charge the storage battery and drive the loads to run.
When a train is operating, the PSFB charger is also to be frequently switched between the three running modes. Correspondingly, a control system of the PSFB charger has to respond to the switchover between the running modes in time, so as to perform switchover between the three control strategies in time. Generally, the three control strategies are under PI (Proportional-Integral) control. If three groups of the same proportional parameters and integral parameters are used, the individuality of each running mode cannot be satisfied, and the technical requirements of controlling both the voltage and the current in a steady state cannot be fulfilled. If three groups of different proportional parameters and integral parameters are used, at the moment of switchover between two control strategies, the proportional parameters and the integral parameters are to be switched quickly, thus leading to overshoot in voltage and current when the system is dynamically adjusted, or even damage in extreme situations.
At present, there is no one control method that can ensure smooth switchover of a PSFB charger for a train between different running modes, and also stable operation of the PSFB charger at the moment of and after the switchover between different running modes.